Inhibitors of proteases are emerging with promising therapeutic uses in the treatment of diseases such as cancers (R. P. Beckett, A. Davidson, A. H. Drummond, M. Whittaker, Drug Disc. Today 1996, 1, 16-26; L. L. Johnson, R. Dyer, D. J. Hupe, Curr. Opin. Chem. Biol. 1998, 2, 466-71; D. Leung, G. Abbenante, and D. P. Fairlie, J. Med. Chem. 2000, 43, 305-341, T. Rockway, Expert Opin. Ther. Patents 2003, 13, 773-786), parasitic, fungal, and viral infections [e.g. schistosomiasis (M. M. Becker, S. A. Harrop, J. P. Dalton, B. H. Kalinna, D. P. McManus, D. P. Brindley, J. Biol. Chem. 1995, 270, 24496-501); C. albicans (C. Abad-Zapetero, R. Goldman, S. W. Muchmore, C. Hutchins, K. Stewart, J. Navaza, C. D. Payne, T. L. Ray, Protein Sci. 1996, 5, 640-52), HIV (A. Wlodawer, J. W. Erickson, Annu. Rev. Biochem. 1993, 62, 543-85; P. L. Darke, J. R. Huff, Adv. Phannacol. 1994, 5, 399-454), hepatitis (J. L. Kim, K. A. Morgenstern, C. Lin, T. Fox, M. D. Dwyer, J. A. Landro, S. P. Chambers, W. Markland, C. A. Lepre, E. T. O'Malley, S. L. Harbeson, C. M. Rice, M. A. Murcko, P. R. Caron, J. A. Thomson, Cell, 1996, 87, 343-55; R. A. Love, H. E. Parge, J. A. Wickersham, Z. Hostomsky, N. Habuka, E. W. Moomaw, T. Adachi, Z. Hostomska, Cell, 1996, 87, 331-342), herpes (W. Gibson, M. R. Hall, Drug. Des. Discov. 1997, 15, 39-47)], and inflammatory, immunological, respiratory (P. R. Bernstein, P. D. Edwards, J. C. Williams, Prog. Med. Chem. 1994, 31, 59-120; T. E. Hugh, Trends Biotechnol. 1996, 14, 409-12,), cardiovascular (M. T. Stubbs, W. A. Bode, Thromb. Res. 1993, 69, 1-58; H. Fukami et al, Current Pharmaceutical Design 1998, 4, 439-453), and neurodegenerative defects including Alzheimer's disease (R. Vassar, B. D. Bennett, S. Babu-Kahn, S. Kahn, E. A. Mendiaz, Science, 1999, 286, 735-41), angiogenesis (Kaatinen M et al, Atherosklerosis 1996, 123 1-2, 123-131) and multiple sclerosis (Ibrahim M Z et al, J. Neuroimmunol 1996, 70, 131-138.
As most proteases bind their substrates in extended or β-strand conformations, good inhibitors must thus be able to mimic such a conformation. β-Hairpin mimetics are thus ideally suited to lock peptide sequences in an extended conformation.
Among proteases, serine proteases constitute important therapeutic targets. Serine proteases are classified by their substrate specificity, particularly by the type of residue found at P1, as either trypsin-like (positively charged residues Lys/Arg preferred at P1), elastase-like (small hydrophobic residues Ala/Val at P1), or chymotrypsin-like (large hydrophobic residues Phe/Tyr/Leu at P1). Serine proteases for which protease-inhibitor X-ray crystal data is available on the PDB data base (PDB: www.rcsb.org/pdb) include trypsin, α-chymotrypsin, γ-chymotrypsin, human neutrophil elastase, thrombin, subtilisin, human cytomegalovirus, proteinase A, achromobacter, human cathepsin G, glutamic acid-specific protease, carbopeptidase D, blood coagulation factorVIIa, porcine factor 1XA, mesentericopeptidase, HCV protease, and thermitase. Other serine proteases which are of therapeutic interest include tryptase, complement convertase, hepatitis C-NS3 protease. Inhibitors of thrombin (e.g. J. L. Metha, L. Y. Chen, W. W. Nichols, C. Mattsson, D. Gustaffson, T. G. P. Saldeen, J. Cardiovasc. Phannacol. 1998, 31, 345-51; C. Lila, P. Gloanec, L. Cadet, Y. Herve, J. Fournier, F. Leborgne, T. J. Verbeuren, G. DeNanteuil, Synth. Comm. 1998, 28, 4419-29) and factor Xa (e.g. J. P. Vacca, Annu. Rep. Med. Chem. 1998, 33, 81-90) are in clinical evaluation as anti-thrombotics, inhibitors of elastase (J. R. Williams, R. C. Falcone, C. Knee, R. L. Stein, A. M. Strimpler, B. Reaves, R. E. Giles, R. D. Krell, Am. Rev. Respir. Dis. 1991, 144, 875-83) are in clinical trials for emphysema and other pulmonary diseases whereas tryptase inhibitors are currently in phase II clinical trials for asthma (C. Seife, Science 1997, 277, 1602-3), urokinase inhibitors for breast cancer, and chymase inhibitors for heart related diseases. Finally, cathepsin G and elastase are intimately involved in the modulation of activities of cytokines and their receptors. Particularly at sites of inflammation, high concentration of cathepsin G, elastase and proteinase 3 are released from infiltrating polymorphonuclear cells in close temporal correlation to elevated levels of inflammatory cytokines, strongly indicating that these proteases are involved in the control of cytokine bioactivity and availability (U. Bank, S. Ansorge, J. Leukoc. Biol. 2001, 69, 177-90). Thus inhibitors of elastase and cathepsin G constitute valuable targets for novel drug candidates particularly for chronic obstructive pulmonary disease (Ohbayashi H, Epert Opin. Investig. Drugs 2002, 11, 965-980).
Of the many occurring proteinaceous serine protease inhibitors, one is a 14 amino acid cyclic peptide from sunflower seeds, termed sunflower trypsin inhibitor (SFTI-1) (S. Luckett, R. Santiago Garcia, J. J. Barker, A. V. Konarev, P. R. Shewry, A. R. Clarke, R. L. Brady, J. Mol. Biol. 1999, 290, 525-533; Y.-Q. Long, S.-L. Lee, C.-Y. Lin, I. J. Enyedy, S. Wang, P. Li, R. B. Dickson, P. P. Roller, Biorg. & Med. Chem. Lett. 2001, 11, 2515-2519), which shows both sequence and conformational similarity with the trypsin-reactive loop of the Bowman-Birk family of serine protease inhibitors. The inhibitor adopts a β-hairpin conformation when bound to the active site of bovine β-trypsin. SFTI-1 inhibited β-trypsin (Ki<0.1 nM), cathepsin G (Ki˜0.15 nM), elastase (Ki˜105 μM), chymotrypsin (Ki˜7.4 μM) and thrombin (Ki˜136 mM).